1. Field of the Invention
This invention pertains to the field of terrain awareness and warning systems employed in aircraft.
2. Description of the Related Art
Beginning in the early 1970's, a number of studies looked at the occurrence of “controlled flight into terrain” (CFIT)-type accidents, where a properly functioning airplane under the control of a fully qualified and certificated crew is flown into terrain (or water or obstacles) with no apparent awareness on the part of the crew. Findings from these studies indicated that many such accidents could have been avoided if a warning device called a ground proximity warning system (“GPWS”) was used. There have been numerous patents issued in the field of GPWS and related art. A sampling of patents issued in the art and related art include U.S. Pat. Nos. 5,839,080; 6,092,009; 6,122,570; 6,138,060; 6,219,592; and 7,145,501.
Advances in technology have permitted vendors and designers of avionics equipment to develop newer type of GPWS that provides greater situational awareness for flight crews. The U.S. Federal Aviation Administration (“FAA”) has classified such systems as Terrain Awareness and Warning Systems (“TAWS”). The advancement of technologies—more precise navigation systems, increased computer memory storage, and better display technology—have allowed further development of in the common features of TAWS: (1) use of airplane position information from the aircraft's navigation system(s), (2) an onboard terrain database, and (3) a means of displaying the surrounding terrain. Aircraft position information from the aircraft's navigation system is fed to a TAWS computer. The TAWS computer compares the airplane's current position and flight path with the terrain database associated with the system. If there is a potential threat of collision with terrain, the TAWS computer sends warning alerts to the airplane's audio system.
There are scenarios for which TAWS has been implemented. These scenarios may be categorized by the flight operations in which aircraft accidents have occurred: departure operations, enroute operations, and arrival operations. First, departure operations could include accidents in which the aircraft does not climb fast enough to clear a terrain cell of interest and in which a pilot has leveled off before the aircraft has achieved the appropriate altitude to clear the terrain. Second, enroute operations could include accidents associated with level flight into terrain and descending flight into terrain. Third, arrival operations could include accidents associated with premature descents and late level-offs in a step down arrival procedure. The embodiments disclosed herein present novel and non-trivial system and methods which address these scenarios.
While traditional terrain avoidance systems have primarily comprised of acquiring the current position (e.g., latitude and longitude) of an aircraft in flight for a navigation system such as a global navigation satellite system (e.g., global positioning system (“GPS”), retrieving terrain data corresponding to the current position from a terrain database, presenting the terrain information on a display unit in the cockpit of the aircraft, and generating warnings to pilots if specified warning criteria have been met, another source of terrain information may be acquired from a forward-looking radar system. A common example of such system is a weather radar system in which weather information in front and below an aircraft may be acquired and ultimately presented on a display unit.
Forward-looking radar systems installed in aircraft are known to those skilled in the art to produce terrain images often referred to as “ground clutter.” While such images are often considered negatively as impairing the quality of the acquired data, the embodiments herein utilize such data to provide an alternate source of terrain information. For instance, the embodiments herein do not require the installation of a terrain database to provide terrain clearance information. In addition, the terrain data received from forward-looking radar systems may be used in conjunction with a terrain database and GPS system to produce a hybrid measurement of terrain data having a higher confidence level than either system can produce separately.